Reliable carbon-neutral power generation system

ABSTRACT

Systems for providing reliable, controllable power without releasing the greenhouse gas carbon dioxide (CO.sub.2) to the environment. Any CO.sub.2 generated is captured and converted to hydrocarbons, which may be used as hydrocarbon feedstock or as additional fuel. Some of these systems can even reduce atmospheric carbon dioxide. The systems may utilize a carbon-neutral energy source.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage entry of PCT/US2008/050805, filedJan. 10, 2008, which claims priority to 60/900,564, filed Feb. 9, 2007and 60/905377, filed Mar. 7, 2007.

RELATED APPLICATIONS

This application is related to commonly owned and currently pendingpatent application “Apparatus and Method for Collecting an AtmosphericGas”, U.S. Patent Application 60/900,564, filed Feb. 9, 2007, which isincorporated herein in its entirety, to the extent that it is notinconsistent with the present disclosure.

FIELD OF THE INVENTION

The present invention relates to systems for providing reliable,controllable output power without releasing the greenhouse gas carbondioxide to the atmosphere. Operation of these systems may even reduceatmospheric carbon dioxide. The systems may utilize a carbon-neutralenergy source, and may regenerate fuel for later use.

BACKGROUND

The Intergovernmental Panel on Climate Change (IPCC) report released bythe United Nations on Feb. 2, 2007 states that it is unequivocal thatclimate change due to global warming is occurring and that it is atleast 90 percent certain that humans are responsible. A major cause ofthis warming is the increased concentration of the “greenhouse gas”carbon dioxide (CO₂) in the atmosphere, primarily due to humans burninghydrocarbon fossil fuels to produce energy for transportation andelectrical power generation. See FIG. 1. To address the problem ofglobal warming, several countries who are signatories of the KyotoProtocol agreement are establishing laws to reduce the rate of carbondioxide emission within their jurisdictions. Several state and localgovernments in the United States of America are also implementing suchlaws. One of the legal approaches being used in Europe and elsewhere isa “cap and trade” system. With this approach, decreasing annual limitsare set on the total amount of carbon dioxide emitted by each company.Companies that go over their annual cap might be fined. However,efficient companies that emit less than their cap amount earn “carboncredits” that can be sold or traded to excess emitters. According to anarticle in the Feb. 14, 2007, edition of the Saint Paul Pioneer Pressnewspaper of Saint Paul, Minn., USA, there are now firms such asLondon-based “Sindicatum Carbon Capital Ltd., which develops projectsthat produce emission credits.” The article also states that “Globalemissions-permit trading was worth about $21.5 billion in the first ninemonths of 2006, almost double the $11 billion in all of the previousyear, the World Bank said in October.”

A Feb. 3, 2007, newspaper article by Thomas H. Maugh II and Karen Kaplanof the Los Angeles Times states that the IPCC report “also said warmingwould continue even in the extremely unlikely event that global carbondioxide could be stabilized at its current level. Such a stabilizationwould require an immediate 70 percent to 80 percent reduction inemissions, said Richard Somerville of the Scripps Institution ofOceanography in San Diego.” The carbon dioxide level persists and buildsup because the main natural mechanism for “permanently” removing carbondioxide from the atmosphere is the process of photosynthesis, in whichplants use energy from sunlight to convert carbon dioxide and water intoplant tissue materials such as sugars and cellulose. The total plantpopulation of the earth cannot consume carbon dioxide at a rate equal tothe current rate of carbon dioxide emission from human activities.Carbon dioxide can be “temporarily” removed from the atmosphere when itdissolves in bodies of water such as the ocean, forming carbonic acid.This carbonic acid may react with certain ions in the water to formrelatively insoluble materials, such as calcium carbonate (limestone).Coral polyp animals use this process to form their coral reef homes.However, excess carbonic acid raises the acidity of the water,endangering the lifeforms living in the bodies of water. Recent“bleaching” of coral reefs has been attributed to this acidification ofthe ocean, accompanied by the water temperature increases due to globalwarming However, if the “carbonated” water warms up or the air pressureabove the water is reduced, some of the carbonic acid decomposes andcarbon dioxide is released back into the air. An example of thisdecomposition process is the CO₂ bubble formation and “fizzing” whichresults from the pressure release upon opening a container of acarbonated beverage.

In order to meet CO₂ emission reduction targets of present or futureregulations such as those based on the Kyoto Protocol, some powergeneration stations are experimenting with an approach called “carbonsequestration.” In this approach, CO₂ gas emitted during the burning ofcoal or other fossil fuels is trapped at the source and pumpedunderground. In favorable locations, this gas could be used topressurize underground petroleum reservoirs, to enhance oil recovery.However, there is no guarantee that the CO₂ will not eventually leakback to the surface and re-enter the atmosphere. Such a sequestrationapproach is proposed by David Keith in the following paper: David W.Keith, Minh Ha-Duong and Joshuah K. Stolaroff (2005). Climate strategywith CO2 capture from the air. Climatic Change, published on line, DOI:Oct. 1, 2007/s10584-005-9026-x Dr. Keith's proposed carbon trapping isbased on reacting CO₂ gas with an NaOH solution, then reacting thissolution with CaO to form lime (calcium carbonate), then heating thelime to release the CO₂ gas again. A large amount of energy is neededfor the heating process, thus reducing the net energy output of thepower generation station.

There is currently a social movement to develop and deploy“carbon-neutral” technologies for energy generation, technologies thatdo not emit carbon dioxide. An example of this would be a wind turbinegenerator. While considerable CO₂ might be emitted generating the energyused in manufacturing a wind turbine, when the final device is inoperation, no additional CO₂ is released. Thus, the manufacturingprocess may be “carbon-positive” (net CO₂ emissions), but the operationof the finished wind turbine is “carbon-neutral”. If the process ofmanufacturing a second turbine uses an amount of energy equal to thelifetime energy output of the first turbine, then both the manufacturingof the second turbine and its total energy output will effectively becompletely “carbon-neutral”. For purposes of this patent application,technologies that are “carbon-neutral” during operation will be referredto as “carbon-neutral” energy sources. Other “carbon-neutral” energysource technologies can include solar photovoltaic, solar thermal,hydroelectric, tidal hydroelectric, wave action hydroelectric (such asthe SEADOG™ pump, U.S. Pat. Nos. 6,953,328 and 7,059,123, available fromIndependent Natural Resources, Inc. (INRI), Eden Prairie, Minn., USA),nuclear, and geothermal. Unfortunately, some carbon-neutraltechnologies, particular solar and wind, are intermittent. Thus, theyare not well suited as the sole power source for applications requiringcontinuous reliability, such as electrical utilities or vehiclepropulsion.

The electrical utilities industry in the United States has its pricesset by a government commission, and must petition the commission toapprove any rate increases. The industry frequently expects any newequipment to last for 50 years in service. State and federal governmentsare discussing legislation that would require electrical utilities toreduce their total CO₂ emission, and to obtain some minimum percentageof their total electrical output from “renewable energy” sources in afew years. Utility company executives are beginning to request that thefederal government establish these laws soon, so the utilities will beable to plan and design equipment that will meet the new standards asthey install their next equipment upgrades. It would be valuable if thenext equipment could be retrofitted into the large installed base ofpower generation equipment, to reduce greenhouse gas emissions ofcurrent equipment. It would also be useful if the new systems couldprovide flexibility to ease the transition from the current installedbase to a future infrastructure based on “renewable energy” sources andmore sustainable systems.

While the electrical utilities industry is currently developingapproaches that may take them at least part way to their CO₂ reductiontargets, the transportation industry, and particularly airplanes andocean-going vessels, have more difficult challenges. Vehicles mustgenerally carry their fuel or energy source with them over longdistances. Batteries or fuel cells may work for automobiles, once thetechnology and the “refueling” infrastructure are developed, but theseenergy sources tend to be heavy, and sometimes bulky. Airlines inparticular require light weight, compact, efficient energy sources, andit is difficult to see how fossil fuels and their accompanying CO₂emissions would be replaced in this industry any time soon. Therefore,the airline industry (and others) will be strongly “carbon-positive” forthe foreseeable future. In “cap and trade” countries, such industrieswill be under pressure to buy increasing amounts of increasinglyexpensive “carbon credits” from other companies. If a “carbon-negative”technology could be developed that would collect CO₂ from the atmosphereand convert the carbon to a useful non-gaseous form, the industries thatare forced to use fossil fuels could use this CO₂ collection/remediationtechnology to offset their emissions, thereby meeting their net CO₂emission cap targets. Such a “carbon-negative” technology has beendescribed in the commonly owned and currently pending patent application“Apparatus and Method for Collecting an Atmospheric Gas”, U.S. PatentApplication 60/900,564, filed Feb. 9, 2007, which is incorporated hereinby reference in its entirety.

Some preliminary efforts have been made at developing technologies thatcould chemically convert greenhouse gases such as CO₂ into othermaterials using process that might be considered carbon-negative. See,for example, U.S. Pat. No. 7,140,181, “Reactor for solar processing ofslightly-absorbing or transparent gases”, Jensen, et al., and U.S. Pat.No. 6,066,187, “Solar reduction of CO.sub.2”, also by Jensen, et al.However, these are energy-intensive, high temperature processes,requiring intense concentrated sunlight and associated expensiveequipment. Furthermore, these patents do not address the problem ofcollecting the greenhouse gas from the atmosphere and concentrating thegas to make the subsequent chemical reaction processes more efficient.

Other interesting related technologies are discussed in the followingdocuments: U.S. Pat. No. 4,478,699, “Photosynthetic solar energycollector and process for its use”, Hallman, et al.; U.S. Pat. No.4,240,882, “Gas fixation solar cell using gas diffusion semiconductorelectrode”, Ang, et al.; and U.S. Pat. No. 4,160,816, “Process forstoring solar energy in the form of an electrochemically generatedcompound”, Williams, et al. These patents also do not adequately addressthe problem of removing the greenhouse gas from the atmosphere.

Thus, as the world seeks to control greenhouse gas concentrations in theatmosphere and to transition to renewable energy sources and a moreenvironmentally sustainable power generation infrastructure, there is aneed for a technology capable of allowing existing fossil fuel basedenergy technologies to be modified to operate with no net greenhouse gasemission, or even to operate with a net reduction of atmosphericgreenhouse gas concentration.

SUMMARY OF THE INVENTION

The present invention allows a power generation facility to collectcarbon-neutral energy intermittently, use this energy to extract CO₂greenhouse gas from the atmosphere, and chemically reduce the CO₂ inorder to locally create fuel for a fossil fuel based power generationsystem that can then provide reliable continuous power. If the fossilfuel based power generation system is a conventional power plant, itwould preferably also be equipped with a device to capture the CO₂generated when burning the fuel, and would recycle this CO₂ through thesame process. Such local generation of fuel would save the cost andassociated greenhouse gas emission of extracting fossil fuels from theearth, refining the fossil fuels, and transporting them to the powerplant location. Some of the CO₂ extracted from the atmosphere would thusbe recycled within the system and would serve as a storage device forthe intermittently-collected carbon-neutral energy. The excess CO₂extracted could be converted into hydrocarbon feedstock for plastics andother products. The carbon-neutral energy could also be used to generateH₂ gas from electrolysis of water. Some of this H₂ could be used tochemically reduce the CO₂ to fuel. Excess H₂ gas could be used to powerhybrid vehicles and fuel cells. Such an integrated system could providea flexible transition technology as society moves from fossil fuel torenewable, carbon-neutral energy sources. The proposed system can removeatmospheric CO₂, produce H₂ fuel for hybrid vehicles and fuel cells,produce hydrocarbon feedstock, and produce fuel for conventional powerplants that preferable have CO₂ recapture equipment. These variousfunctions can be performed in variable proportions as needed. Suchhybrid power generation systems would provide a carbon-neutral, or evencarbon-negative, technology having the continuous reliability of currentfossil fuel based power generation technologies.

One aspect of the present invention is a power generation system havinga carbon-neutral energy source and a fuel production system powered atleast in part by the carbon-neutral energy source, in which the fuelproduction system can produce at least one fuel using air, water, orboth as raw materials. The system also includes a power generationsubsystem that can generate power using energy from the produced fuel.

The invention may further include a capture device that captures atleast one chemical reaction product, such as carbon dioxide, that isproduced by burning or using the fuel. This captured reaction productmay be used to make additional fuel. This fuel could be hydrogen orhydrocarbons. The capture device may include a cooled device forcondensing gases to liquids or solids. The reaction products may reachthe cooled device by passing through a counter-flow heat exchanger.

The invention may be part of a mobile system, such as a partiallysolar-powered automobile, ship, or other vehicle. The power generationsystem of this invention may also include at least one fuel cell.

Another aspect of this invention is a power generation system thatprovides reliable, controllable power without releasing carbon dioxidegreenhouse gas to the atmosphere. This embodiment has a power generationsubsystem that uses energy from chemical reactions of a fuel, a capturedevice that captures at least one chemical reaction product (such asCO₂) from burning or using the fuel, and a fuel production system thatcan produce additional fuel using the captured reaction product as theprimary raw material. The capture device may include a cooled device forcondensing gases to liquids or solids. The reaction products may reachthe cooled device by passing through a counter-flow heat exchanger.

BRIEF DESCRIPTION OF THE FIGURES

The invention may be more completely understood and appreciated inconsideration of the following detailed description of variousembodiments of the invention in connection with the accompanyingdrawings, in which:

FIG. 1 schematically illustrates the net increase of the greenhouse gascarbon dioxide in the atmosphere as a result of burning hydrocarbonfuels to produce energy.

FIG. 2 shows a schematic diagram of a CO₂ conversion system includingthe CO₂ capture device of this invention.

FIG. 3 shows a closed system based on water as a working fluid, in whichenergy but not matter crosses the system boundary.

FIG. 4 shows a closed system based on water and carbon dioxide asworking fluids, in which energy but not matter crosses the systemboundary.

FIG. 5 schematically illustrates a system in which air, water,hydrocarbon fuels, and a carbon-neutral energy source are used toprovide reliable, controllable output power without releasing carbondioxide to the atmosphere.

FIG. 6 shows a cross-section view of a solar-powered gas capture device.

FIG. 7 schematically illustrates a cross-section of a power generationsystem having two gas capture devices receiving reaction product gasesfrom the fuel reaction chamber by way of a counter-flow heat exchanger.

FIG. 8 shows a cross-section of the counter-flow heat exchanger of FIG.7, viewed at line AA′ of FIG. 7.

The same reference numeral used in multiple figures refers to the sameor similar elements having the same or similar properties andfunctionalities.

DETAILED DESCRIPTION

The present invention includes a carbon-neutral energy source thatprovides at least a portion of the energy required to operate an “aircapture” device that can collect CO₂ from the earth's atmosphere, asshown in the upper right of FIG. 2. One example of such a device is theNaOH, CaCO₃ cycle device proposed by Prof David Keith in his paper“Climate strategy with CO2 capture from the air”, mentioned above.Another example is the invention disclosed in commonly owned andcurrently pending patent application “Apparatus and Method forCollecting an Atmospheric Gas”, 60,900,564, filed Feb. 9, 2007, oneembodiment of which is described below.

In addition, the present invention may also use the same or a differentcarbon-neutral energy source to generate H₂ gas from water in, forexample, an electrolytic cell or a reversible hydrogen fuel cell, asshown in the upper left of FIG. 2. The H₂ gas may be used as a fuel, ormay be chemically combined with the captured CO₂ in a reduction chamberto produce hydrocarbon fuels or hydrocarbon feedstock, as shown in thelower portion of FIG. 2.

The present invention also includes a power generation subsystemreceiving energy from a fuel reaction chamber capable of using eitherthe generated H₂ gas or the hydrocarbon fuel to generate power. The fuelreaction chamber optionally is coupled with an “air capture” device thatcan collect CO₂ from the combustion products produced by the fuelreaction chamber if it is using hydrocarbon fuel. The “air capture”device may be the same device that is used to collect CO₂ from theearth's atmosphere, or it may be a separate device. The power generationsubsystem could be, for example, a fossil fuel based electrical utilitypower plant, an internal combustion engine, the engine of a hydrogenpowered vehicle, or a hydrogen fuel cell.

A first embodiment of the present invention is shown in FIG. 3. This isa “closed system”, in which no material need be transferred into or outof the system. Water (H₂O) serves as the “working fluid” for the system.A carbon-neutral energy source, which may be intermittent, is used topower a hydrogen extractor, such as an electrolytic cell, that separateswater into hydrogen and oxygen. These materials are stored in respectivehydrogen and oxygen reservoirs. As energy is needed, the hydrogen andoxygen are fed to a fuel reaction chamber, where they react to reformwater and produce a continuous or controllable energy output. The wateris returned to the hydrogen extractor to continue the cycle. Thus, thissystem collects intermittent, unreliable energy as available from acarbon-neutral source, stores the energy as “potential chemical energy”in the form of separated hydrogen and oxygen, and releases the energy ata desired rate as a controllable energy output. In FIG. 3, the closedmaterial system is shown within the boundary marked by the largestrectangle. Energy from a carbon-neutral energy source enters the closedsystem at the left of the diagram, as indicated by the dashed arrow. Atthe right side of the diagram, a controllable energy output leaves or isgenerated by the system, as indicated by the second dashed arrow. Thesystem of FIG. 3 might be used in a mobile system, such as asolar-powered automobile or an ocean-going vessel using solar or windenergy, or both.

FIG. 4 shows a second “closed system” embodiment of the invention, inwhich both water and carbon dioxide may be considered to be the “workingfluids”. As in FIG. 3, the closed material system is shown within theboundary marked by the largest rectangle. Again, a carbon-neutral energysource, which may be intermittent, is used to power a hydrogenextractor, such as an electrolytic cell, that separates water intohydrogen and oxygen. These materials are stored in respective hydrogenand oxygen reservoirs. However, hydrogen may be further reacted withcarbon dioxide in a carbon reduction chamber to produce varioushydrocarbon fuels, which are then stored in a hydrocarbon reservoir.(The carbon reduction chamber is so named because the carbon in carbondioxide undergoes chemical reduction to a lower oxidation state in thesereactions.) Example chemical reactions include the Sabatier methanationreaction and the reverse water-gas shift reaction (WGS), as described inthe paper “Carbon Dioxide Conversions in Microreactors”, by D. P.VanderWeil, et al., of Pacific Northwest National Laboratory Thehydrocarbons produced in the carbon reduction chamber may be liquids orsolids, and thus would require much less storage space than hydrogen andcarbon dioxide gases. As energy is needed, the hydrocarbons, hydrogen,or both, may be combined with oxygen in the fuel reaction chamber toproduce a controllable energy output. The fuel reaction produces water(probably as vapor) and carbon dioxide, which are collected and recycledwithin the system. Energy from a carbon-neutral energy source enters theclosed system at the left of the diagram, as indicated by the dashedarrow. At the right side of the diagram, a controllable energy outputleaves or is generated by the system, as indicated by the second dashedarrow.

FIG. 2 shows a group of interconnected processes that use acarbon-neutral energy source, air, and water (the water being eitherextracted from the air, e.g., as described in detail below in FIGS. 6and 7, or from local sources) to remove the greenhouse gas CO₂ from theatmosphere (or from gaseous combustion products such as those generatedin the fuel reaction chamber of FIG. 4) and to chemically convert thegas to other chemical compounds or forms of carbon that do notcontribute to climate change. These other chemical forms of carbon maybe more compact for transport, and may be useful hydrocarbon feedstocksfor producing polymers, medicines, (carbon-positive) fuels, or evenfoodstuffs such as sugars and amino acids. In FIG. 2, a known quantityof relatively pure CO₂ is obtained from a gas collection system such asthe one shown in FIG. 6 or 7. The CO₂ could be collected in reservoir170 of FIG. 6. Also, water obtained from the gas collector in FIG. 6(e.g., in auxiliary reservoir 171) or from other sources is provided toan electrolysis cell, the cell being powered by a carbon-neutral energysource, possibly the same source that is also used to power the gascollector of FIG. 6. Auxiliary reservoir 171 in FIG. 6 could be such anelectrolysis cell. The electrolysis cell splits the water into itselemental components, hydrogen and oxygen, by any of a variety of meanscommonly known in the art, as shown in equation (1) below.2 H₂O+energy=>2 H₂+O₂  (1)

A known quantity of the generated hydrogen is then collected andcombined with a known amount of CO₂in a reaction chamber. Collectionchamber 130 or reservoir 170 in FIG. 6 could also serve as such areaction chamber. (The generated hydrogen gas could be made to flow backthrough the collection chamber 130 to reservoir/reaction chamber 170, ora cross-connect pipe could be supplied connecting chambers 171 and 170.)Energy from a carbon-neutral energy source is then applied to thereaction chamber, in the form of one or more of heat, pressure,electromagnetic radiation, or an electric spark/arc, to initiate achemical reaction between the hydrogen and the carbon dioxide.Optionally, other materials such as nitrogen gas may be introduced intothe reaction chamber at some stage in the process. A variety of usefulchemical compounds may be produced in the reaction chamber, dependingon:

-   -   1) the reaction conditions;    -   2) the relative amounts of hydrogen and carbon dioxide; and    -   3) the presence of any catalytic species.

For example, the hydrogen could reduce the CO₂ to elemental carbon, C,the material of graphite and diamonds, as shown in equation 2.2 H₂+CO₂+energy=>2 H₂O+C  (2)

Varying ratios of H₂ and CO₂ under appropriate reaction conditions canalso produce a range of other useful hydrocarbons, as shown below.H₂+CO₂+energy=>HCOOH (formic acid)  (3)2 H₂+CO₂+energy=>H₂O+H₂CO (formaldehyde)  (4)3 H₂+CO₂+energy=>H₂O+H₃COH (methyl alcohol)  (5)4 H₂+CO₂+energy=>2 H₂O+CH₄ (methane, natural gas)  (6)

(Equation 6 is the Sabatier methanation reaction mentioned above.)

Under appropriate conditions, formaldehyde from equation 4 could beconverted to polyoxymethylene, a polymer having excellent mechanical andhigh temperature properties, sold under trade names such as Delrin. Seeequation (7) below.H₂ +nH₂CO=>H—[CH₂—O—]_(n)—H (polyoxymethylene)  (7)

As suggested above, introducing controlled amounts of atmosphericnitrogen gas or other nitrogen compounds into the reaction chamber wouldpermit the synthesis of an even broader range of organic compounds,including foodstuffs such as amino acids.

FIG. 5 shows an “open system” embodiment of the present invention, inwhich matter can also pass into and out of the system. The largestrectangle marks the boundary of the system. In addition to the energyinput from a carbon-neutral energy source, as indicated at the top ofthe diagram, this system also uses material inputs of air, water, andoptionally hydrocarbon fuels, as indicated along the left side of thediagram by the dotted arrows. In addition to the controllable energyoutput indicated by the dashed arrow at the bottom of the diagram, thissystem also can provide possible outputs of hydrogen (for, e.g., forhydrogen powered vehicles), purified oxygen (for possible medical uses,underwater breathing apparatus, welding, etc.), and optionallyhydrocarbon feedstock (for making plastics, medicines, foodstuffs,etc.), as indicated by the dotted output arrows on the right side of thediagram. It will be noted that this system can remove carbon dioxidefrom the atmosphere, and can also operate using fossil fuels, withoutreleasing carbon dioxide to the atmosphere in either case. The relativeinputs to the system can be adjusted to produce the desired ratio ofcontrollable energy output, removal of carbon dioxide from theatmosphere, and production of hydrogen for, e.g., hydrogen poweredvehicles. All three of these functions may be required in variousproportions as society addresses climate change and transitions to moresustainable infrastructure.

The system in FIG. 5 will now be described in more detail. Water isinitially supplied from outside the system to a hydrogen extractor, suchas an electrolytic cell, that is powered at least in part by acarbon-neutral energy source. The hydrogen extractor separates the waterinto hydrogen and oxygen, which may be stored in respective reservoirs.Also, carbon dioxide from the air is supplied to the system, possiblyafter being captured and concentrated by means of a CO₂ capture devicethat will be described later. The CO₂ is then reacted with hydrogen fromthe hydrogen reservoir in a carbon reduction chamber to producehydrocarbons, which may then be stored in an optional hydrocarbonreservoir. These hydrocarbons may be used as fuel for the next stage ofthe system, be extracted for use as hydrocarbon feedstock, or both.Next, the fuel, which may be hydrocarbons, hydrogen, or both, is sent tothe fuel reaction chamber, where it is combined with oxygen (optionallyfrom the oxygen reservoir) to produce energy, which can provide acontrollable energy output. The fuel reaction chamber converts the fuelto water and CO₂ (if hydrocarbon fuels are used). The water and CO₂ canbe recovered and recycled back into the system by means of a CO₂ capturedevice such as the one described later in this application. Some of theenergy produced may be used to power internal processes within thesystem, such as the hydrogen extractor, the carbon reduction chamber,the CO₂ capture device, and the fuel reaction chamber itself Duringsystem startup or at times when insufficient fuel reserves have beenbuilt up using the carbon-neutral energy source, it may be necessary tosupply external hydrocarbon fuels to the system. However, the CO₂capture device assures that no CO₂ greenhouse gas will be released tothe atmosphere by the operation of this system.

One embodiment of the CO₂ capture device of FIG. 5 is the inventiondescribed in commonly owned and currently pending patent application“Apparatus and Method for Collecting an Atmospheric Gas”, U.S. PatentApplication 60/900,564, filed Feb. 9, 2007, one embodiment of which isshown in FIG. 6. The CO₂ capture device shown in FIG. 6 removes CO₂ fromthe atmosphere (or from a gas stream) by taking advantage of thedifference in condensation temperatures of the gases and vapors in theatmosphere. At normal atmospheric pressure, water vapor normallycondenses to a liquid at some temperature below room temperature (thedew point), and solidifies to ice at 0° C. CO₂ condenses directly to asolid (“dry ice”) at −79° C., and converts back to a gas (sublimes) whenheated above that temperature. O₂ and N₂ condense to liquids at −183° C.and −196° C., respectively. Thus, if air comes in contact with a surfacehaving a temperature slightly below −79° C., any H₂O and CO₂ in the airwill deposit on the surface as a mixture of ice and dry ice. These twocomponents could be separated by a 2-stage cooling process. If the airfirst comes in contact with a surface having a temperature between thedew point and 0° C., the water vapor would condense out as a liquid,which could be drained away, and the remaining air would now be “dry”.If the dry air then comes in contact with a surface having a temperatureslightly below −79° C., relatively pure CO₂ would condense on thesurface. This collected CO₂ could then be stored or chemically reactedto remove this greenhouse gas from the atmosphere.

FIG. 6 illustrates a first embodiment of a CO₂ capture device 100 foruse with the present invention. The CO₂ capture device 100 shown in thisfigure includes an optional “carbon-neutral” energy source, in this casea photovoltaic solar panel 101, although the CO₂ capture device shown inFIG. 5 would not need to be directly connected to the carbon-neutralenergy source. A suitable solar panel would be one or an array ofSunPower model SPR-90, available from SunPower Corporation, Sunnyvale,Calif., USA. Solar panel 101 receives electromagnetic energy 103 from asource 104, such as the sun. Panel 101 converts electromagnetic energy103 to electrical energy, which powers cooling unit 110. In thisexample, cooling unit 110 is shaded from direct sunlight by solar panel101, thus reducing the heat load on cooling unit 110 and making thesystem more efficient. If the target gas to be collected is CO₂, coolingunit 110 must be capable of cooling condenser 120 to less than −79° C.when supplied with adequate power. The cooling unit could be selectedfrom any of a variety of technologies, such as Joule-Thomson coolers,Peltier coolers, Stirling coolers, pulse tube cryocoolers,thermoelectric coolers, etc. When the condenser is at a temperature lessthan −79° C., carbon dioxide (and any water vapor) from the air incontact with the condenser will form a coating of deposited dry ice (andice) on the surface of the condenser.

The chilled condenser 120 is enclosed in a collection chamber 130 thathas at least one gas entrance port 134, and optionally one or more gasexit ports 135. Collection chamber 130 may also have an extraction port138 to facilitate removal of the collected target gas from collectionchamber 130. Gas entrance port 134 may function as a check valve,opening to allow air flow into collection chamber 130 when the pressureoutside 130 is greater than the pressure inside, but closing to form anairtight seal when the pressure inside chamber 130 is greater than theair pressure outside. When cooling unit 110 is energized and condenser120 is cooled, the air within the collection chamber will be cooled andwill contract, reducing the pressure within collection chamber 130 belowthe pressure of the outside air (assuming valves 135 and 138 areclosed), causing a check valve at gas entrance port 134 to open andallow more air to flow into collection chamber 130. The target gas(e.g., CO₂) in the added air will condense as a liquid or solid on thecondenser, further reducing the interior pressure in collection chamber130, continuing the process. (Alternatively, valves 134 and 135 may beheld open, allowing a continuous flow of gas past the condenser forcapturing CO₂.) If condenser 120 is then allowed to warm above thecondensation temperature of the target gas, either for an intentionalpurge cycle or due to reduced power input to cooling unit 110 (e.g., atnight for a solar powered unit), some of the condensed target gas willre-vaporize, raising the pressure in collection chamber 130, clampingthe check valve at gas entrance port 134 shut, and trapping the targetmaterial in collection chamber 130. Optional extraction port 138 mayinclude a check valve that opens when the pressure inside collectionchamber 130 is greater than the pressure on the other side of extractionport 138, thus allowing the collected target material to be directedinto a removable container or a permanently attached plumbing system.Alternatively, if the target gas is being condensed to a liquid ratherthan a solid, extraction port 138 may include a liquid “trap” seal madeof an “S”-shaped pipe, similar to the plumbing traps used under alavatory sink

Referring again to FIG. 6, an embodiment having both a gas entrance port134 and at least one gas exit port 135 can be employed, if it is desiredto achieve a greater collection rate of the target gas by causing acontinuous flow of air through collection chamber 130 past condenser120. For this embodiment, entrance port 134 and exit port 135 arenormally open when condenser 120 is at or below a desired condensationtemperature, and are sealed when condenser 120 is above the desiredtemperature. To minimize energy usage, the valves in entrance port 134and exit port 135 could contain bistable valves connected to a valveactuator and a passive temperature sensor that monitors the condensertemperature. Alternatively, entrance port 134 and exit port 135 couldcontain valves that are held open (e.g., by solenoids) while solar panel101 is generating sufficient electrical energy, but that close and sealwhen the electrical output drops below some minimum level. In FIG. 6,collection chamber 130 is arranged with entrance port 134 low on oneside of the chamber and exit port 135 high on the other side of thechamber, to encourage increased air flow due to natural convection.Additionally, exit port 135 is located closer than entrance port 134 tosolar panel 101, which is heated by direct sunlight. This furtherenhances the natural convection flow through collection chamber 130, bymaking air high in the chamber near the exit port warmer. Alternatively,a fan, air pump, or other air flow enhancing device may be included withCO₂ capture system 100.

FIG. 6 also shows a method of collecting water vapor from the atmosphere(or from the effluent gases from the fuel reaction chamber in FIG. 5)and separating it from the CO₂. To facilitate the collection andseparation of water vapor, this CO₂ capture device also includes anoptional auxiliary extraction port 139 and a precondenser 140. Items 139and 140 may be located in collection chamber 130, or they may both belocated in a separate precondenser chamber 150. If it is desired toseparately collect water vapor and CO₂, or to obtain CO₂ that isrelatively free of water, precondenser 140 would be connected to coolingunit 110 and maintained at a temperature between the dew point and −79°C., and preferably between the dew point and 0° C. Precondenser 140could be a screen or grid structure, or a series of baffles, thatprovide significant cold surface area for condensing water vapor, butthat still allow adequate air flow to and through the collection chamber130. Water vapor condensing on precondenser 140 as liquid water woulddrain down to the bottom of the chamber 130 or 150, where it could beremoved through an extraction port 138 or 139. Optional reservoir 170and auxiliary reservoir 171 could receive and contain CO₂ fromextraction port 138 and water from auxiliary extraction port 139,respectively. If an auxiliary extraction port 139 is used, it could be adrain with a liquid “trap”, as described above for item 138. The waterremoved through auxiliary extraction port 139 could be routed to thehydrogen extractor of FIG. 5 to undergo chemical reactions powered bythe same or a different carbon-free energy device.

An optional energy storage unit 160, such as a battery or a hydrogenfuel cell, is also shown in FIG. 6. Energy storage unit 160 may collectand store excess energy generated by the carbon-free energy source, andthen may release this energy to continue operation of the gas capturesystem 100 when the primary carbon-free energy source output is low(e.g., on partly cloudy days or at night, for a solar panel.)

The fuel reaction chamber in FIG. 5 may generate significant heat,particularly if it uses an exothermic reaction such as combustion. Theenergy released in the fuel reaction chamber may, for example, operatethe power generation subsystem by boiling water to produce steam, whichthen turns a turbine generator to produce electricity, as the steam isturned back into water, which is then boiled again according to athermodynamic Carnot cycle. The generated heat may also be used to helpoperate other portions of the system, such as the carbon reductionchamber. Similarly, the generated electricity may be used to power otherportions of the system, such as the hydrogen extractor, the CO₂ capturedevice, and any necessary sensors, pumps, and valves needed to transportmaterials between various portions of the system. The CO₂ capture deviceof FIG. 6 requires a refrigeration unit to condense CO₂ and, optionally,water vapor. The CO₂ capture device of FIG. 6 could be arranged toreceive the exhaust gases from a combustion fuel reaction chamber bypassing the hot exhaust gases through a counter-flow heat exchanger(FIG. 7) to the cold precondenser 140 and condenser 120, where the watervapor and CO₂ would be condensed and collected. Any remaining chilledgases from the exhaust gas, such as nitrogen or unreacted oxygen, wouldthen be fed back through the counter-flow heat exchanger to cool theincoming exhaust gases. The counter-flow heat exchanger minimizes wastedenergy, by not requiring excessive cooling power to chill theprecondenser 140 and condenser 120. Also, to the extent that theprecondenser 140 is below ambient temperature, the energy efficiency ofthe Carnot cycle of the power generation subsystem may be increased byusing the condensed water from the precondenser as a heat sink for theCarnot cycle engine. It should be mentioned here that each of theinternal processes and devices in this system will have less thanperfect efficiency, and will represent some energy loss. That loss mustbe made up by the carbon-neutral energy source, or by the chemicalenergy available from any optional external hydrocarbon fuels providedto the system. This system is not single-mindedly designed to extractthe maximum energy from fossil fuel, regardless of the environmentalconsequences. The goal of this system is to sustainably providereliable, controllable power without releasing CO₂ greenhouse gas to theatmosphere, and preferably, to actually cause a net decrease in theamount of atmospheric CO₂. Useful byproducts of the system, produced incontrollable variable amounts, may be sold to offset the added cost ofthe system. For example, a “hybrid” electric power station based on thesystem in FIG. 5 could not only produce electrical power, but could alsosell hydrogen gas and hydrocarbon fuels for vehicles, hydrocarbonfeedstock, and oxygen gas for welding or medical uses.

A diagram of a power plant embodiment of this invention using acounter-flow heat exchanger is shown in FIG. 7. In this system, the fuelreaction chamber 275 receives oxygen and fuel, which may be hydrogen,hydrocarbons, or both. The oxygen and hydrogen may be supplied from ahydrogen extractor, as shown in FIGS. 3-5. The fuel chemically reactswith oxygen (e.g., by combustion) to produce heat and reaction products,such as water vapor and carbon dioxide. A diluent or carrier gas such asnitrogen may also be present. The hot reaction products leave the fuelreaction chamber and pass through a steam generator 280, where some ofthe thermal energy of the reaction products is used to boil water toproduce steam. This steam may be used as the working fluid in a Carnotcycle process, as indicated by the closed loop including the steamgenerator 280, turbine 281, steam condenser 282, and pump 283. The steamimparts some of its thermal energy to the turbine blades as kineticenergy, causing the turbine shaft to rotate, allowing the turbine topower an electrical generator or a mechanical drive shaft. The steamthat has passed through the turbine 281 is then cooled and re-condensedto liquid water in the steam condenser 282, thus reducing the pressurein the steam condenser and causing more steam to blow through theturbine, due to the pressure difference across the turbine. Thecondensed water is then pumped back into the steam generator 280 by pump283, to repeat the cycle.

In FIG. 7, after the reaction products have given up some of theirthermal energy in the steam generator 280, they are then sent through acounter-flow heat exchanger 285 toward the CO₂ capture device(s) 200,200′, which are similar to the device shown in FIG. 6. The CO₂ capturedevices in FIG. 7 also include precondensers to collect and remove watervapor from the reaction product gases. FIG. 7 shows two CO₂ capturedevices 200, 200′ connected in parallel, such that the condenser 220 ofone capture device can be held at a temperature below −79° C. tocondense and capture CO₂ while the other capture device is being shutoff from the incoming reaction products and warmed above −79° C. torelease the collected CO₂, to force the CO₂ onward through thecounter-flow heat exchanger 285 to the carbon reduction chamber 290. Thegas flows are controlled by a variety of valves, such as gas exit portvalve 235′, and monitored by temperature and pressure sensors, such aspressure sensor 273. Since the released CO₂ will still be cold, passingit through the counter-flow heat exchanger will help warm the CO₂ to thetemperature of the carbon reduction chamber, while at the same timepre-cooling the reaction product gases that are heading towards theother CO₂ capture device. The CO₂ capture devices 200, 200′ in FIG. 7are also shown having bypass outlets, through which any excess oxygen,unreacted fuel, uncondensed reaction products, or diluent gas can alsopass through the counter-flow heat exchanger back into the fuel reactionchamber. This counter-flow arrangement minimizes the energy needed tocool or heat the materials for the next steps in the process. Across-section of the counter-flow heater exchanger 285 in FIG. 7, takenalong line AA′, is shown in FIG. 8. Multiple tubes, or tubes ofdifferent shapes, may be substituted for either or both of the innertubes of the heat exchanger carrying CO₂ and returned gases, in order toincrease the area for heat transfer, thus improving the efficiency ofthe heat exchanger.

The chemical processes in the carbon reduction chamber 290 willtypically be endothermic. Therefore, the carbon reduction chamber 290 isshown adjacent to the fuel reaction chamber 275, so the carbon reductionchamber processes can make use of the heat and high temperatures (andperhaps high pressures) produced in the fuel reaction chamber.

In the carbon reduction chamber 290 of FIG. 7, the collected CO₂ isreacted with hydrogen to produce hydrocarbons, which are then stored inthe hydrocarbon reservoir 295. Depending on the chemical reactionsoccurring in the carbon reduction chamber, some H₂O may also beproduced. It may be desirable to separate this water from thehydrocarbons. However, if the water is left with the hydrocarbons and ispumped into the fuel reaction chamber, the water will eventually becollected at the precondensers of the CO₂ capture devices and removedfrom this portion of the system. Since the water collected at theprecondensers will be relatively cool, it would provide an excellentheat sink material for the steam condenser 282 of the Carnot cycle powergeneration subsystem.

The system of FIG. 7 could be combined with a carbon-neutral energysource and a hydrogen extractor, as shown in FIG. 5. Such a system couldbe used to generate power, to remove the greenhouse gas carbon dioxidefrom the atmosphere, or both. In addition, such a system could providean economically important source of hydrocarbon feedstock, hydrogen forhydrogen-powered vehicles, oxygen for medical or welding uses, etc.

While specific examples of the invention are described in detail aboveto facilitate explanation of various aspects of the invention, it shouldbe understood that the intention is not to limit the invention to thespecifics of the examples. Rather, the intention is to cover allmodifications, embodiments, and alternatives falling within the spiritand scope of the invention as defined by the appended claims.

What is claimed is:
 1. A power generation system comprising: a powergeneration subsystem capable of providing controllable energy output; afuel reaction chamber in which energy to be provided to the powergeneration subsystem is obtained by oxidation of at least onehydrocarbon fuel, wherein said oxidation produces at least carbondioxide (CO₂); a CO2 capture device capable of capturing at least aportion of any carbon dioxide produced by the oxidation of the at leastone hydrocarbon fuel in the fuel reaction chamber; a carbon reductionchamber adapted to receive CO₂ from the CO₂ capture device and to reducethe chemical oxidation state of the carbon atoms of the received CO₂;and a carbon-neutral energy source from which energy can be obtainedwith essentially no release of carbon dioxide to the environment duringextended operation of the carbon-neutral energy source wherein energyfrom the carbon-neutral energy source is used in the carbon reductionchamber, directly or indirectly, to reduce the chemical oxidation stateof carbon atoms of the carbon dioxide in the carbon reduction chamber.2. The power generation system of claim 1, wherein reducing the chemicaloxidation state of the carbon atoms of the carbon dioxide in the carbonreduction chamber produces at least one second-generation hydrocarbonfuel.
 3. The power generation system of claim 2, wherein the powergeneration system is adapted to direct the at least onesecond-generation hydrocarbon fuel to the fuel reaction chamber.
 4. Thepower generation system of claim 3, wherein the carbon-neutral energysource is an intermittent energy source for which the timing and amountof energy availability is not readily controlled, and essentially nocarbon dioxide is released to the environment during extended operationof the power generation system.
 5. A method of providing controllableenergy output with significantly reduced or minimal release of carbondioxide to the environment, comprising the steps of: providing the powergeneration system of claim 3; providing a quantity of oxygen and of atleast one first-generation hydrocarbon fuel to the fuel reactionchamber; causing oxidation of the at least one first-generationhydrocarbon fuel in the fuel reaction chamber, thus producing carbondioxide and providing energy to the power generation subsystem;capturing with the CO₂ capture device the majority of the carbon dioxideproduced by the oxidation of the at least one first-generationhydrocarbon fuel; delivering a portion of the captured carbon dioxide tothe carbon reduction chamber; obtaining energy from the carbon-neutralenergy source; using the energy from the carbon-neutral energy source,directly or indirectly, to reduce the chemical oxidation state of thecarbon atoms of the carbon dioxide in the carbon reduction chamber, thusproducing at least one reduced carbon chemical species; and, providing aquantity of the at least one reduced carbon chemical species to the fuelreaction chamber and oxidizing the at least one reduced carbon chemicalspecies, which thus serves as a second-generation hydrocarbon fuel. 6.The power generation system of claim 1, wherein the power generationsubsystem is a portion of an electrical utility power plant.
 7. Thepower generation system of claim 1, wherein reducing the chemicaloxidation state of carbon in the carbon dioxide in the carbon reductionchamber produces chemicals comprising at least one chemical selectedfrom the group consisting of elemental carbon, methane, methyl alcohol,formaldehyde, formic acid, and polyoxymethylene.
 8. The power generationsystem of claim 1, further comprising a hydrogen extractor that providesa source of hydrogen atoms to the carbon reduction chamber
 9. The powergeneration system of claim 1, further comprising at least oneelectrolytic cell.
 10. The power generation system according to claim 1,further comprising a device adapted to capture at least one of water oroxygen that has been chemically generated within the system.
 11. Thepower generation system according to claim 1, wherein the powergeneration system has a boundary enclosing an interior, the interiorcontaining the power generation system's working fluids CO₂ and H₂O, andfurther wherein the power generation system operates as an essentiallyclosed system with respect to the materials CO₂, H₂, O₂, H₂O, andhydrocarbons, such that essentially none of these materials pass throughthe boundary of the power generation system into or out of its interiorduring normal operation of the power generation system.
 12. The systemaccording to claim 1, wherein the system generates hydrocarbonfeedstock.
 13. A power generation system as in claim 1, wherein the CO₂capture device comprises a cooled gas condenser.
 14. A power generationsystem as in claim 1, wherein the system is mobile.
 15. A powergeneration system as in claim 1, further comprising a fuel cell.
 16. Amethod of providing controllable energy output with significantlyreduced or minimal release of carbon dioxide to the environment,comprising the steps of: providing the power generation system of claim1; providing a quantity of oxygen and of at least one hydrocarbon fuelto the fuel reaction chamber; causing oxidation of the at least onehydrocarbon fuel in the fuel reaction chamber, thus producing carbondioxide and providing energy to the power generation subsystem;capturing with the CO₂ capture device the majority of the carbon dioxideproduced by the oxidation of the hydrocarbon fuel; delivering a portionof the captured carbon dioxide to the carbon reduction chamber;obtaining energy from the carbon-neutral energy source; and using theenergy from the carbon-neutral energy source, directly or indirectly, toreduce the chemical oxidation state of the carbon atoms of the carbondioxide in the carbon reduction chamber, thus producing at least onereduced carbon chemical species.
 17. The method of claim 16, wherein theat least one first-generation hydrocarbon fuel is a fossil fuel.
 18. Themethod of claim 16, wherein the at least one first-generationhydrocarbon fuel comprises at least one of coal, oil, natural gas,diesel fuel, gasoline, aviation fuel, or wood.
 19. The method of claim16, wherein the CO₂ capture device comprises a cooled gas condenser, andfurther wherein the carbon dioxide reaches the cooled gas condenser byway of a counter-flow heat exchanger.
 20. The method of claim 16,wherein at least one of heat or pressure from the oxidation of the atleast one hydrocarbon fuel in the fuel reaction chamber is used toassist the reduction of the oxidation state of the carbon atoms of thecarbon dioxide in the carbon reduction chamber.
 21. The method of claim16, wherein the step of using the energy from the carbon-neutral energysource, directly or indirectly, to reduce the chemical oxidation stateof carbon atoms of the carbon dioxide in the carbon reduction chamber,thus producing at least one reduced carbon chemical species, comprisescarrying out at least one of the Sabatier methanation reaction or thereverse water-gas shift reaction.
 22. The method of claim 16, furthercomprising the step of providing a quantity of the at least one reducedcarbon chemical species to the fuel reaction chamber and thereinoxidizing the at least one reduced carbon chemical species, which thusserves as additional hydrocarbon fuel.
 23. The power generation systemof claim 1, further wherein at least one of heat or pressure from theoxidation of the at least one hydrocarbon fuel in the fuel reactionchamber is used to assist the reduction of the oxidation state of thecarbon atoms of the carbon dioxide in the carbon reduction chamber. 24.The power generation system of claim 1, wherein the carbon reductionchamber is adapted to carry out at least one of the Sabatier methanationreaction or the reverse water-gas shift reaction.
 25. The powergeneration system of claim 1, wherein the carbon-neutral energy sourcecomprises at least one of solar photovoltaic, solar thermal,hydroelectric, tidal hydroelectric, wave action hydroelectric, nuclear,or geothermal.
 26. A controllable power generation system capable ofoperating with essentially no release of carbon dioxide greenhouse gasto the environment, comprising: a power generation subsystem capable ofproviding controllable energy output; a fuel reaction chamber in whichenergy to be provided to the power generation subsystem is obtained byoxidation of at least one hydrocarbon fuel, wherein said oxidationproduces at least carbon dioxide (CO2); a CO2 capture device capable ofcapturing at least a portion of any carbon dioxide produced by theoxidation of the at least one hydrocarbon fuel in the fuel reactionchamber; a carbon reduction chamber adapted to receive CO2 from the CO2capture device and to reduce the chemical oxidation state of the carbonatoms of the received CO2; and a carbon-neutral energy source from whichenergy can be obtained with essentially no release of carbon dioxide tothe environment during extended operation of the carbon-neutral energysource, wherein energy from the carbon-neutral energy source is used inthe carbon reduction chamber, directly or indirectly, to reduce thechemical oxidation state of carbon atoms of the carbon dioxide in thecarbon reduction chamber, and further wherein the power generationsystem has a boundary enclosing an interior, the interior containing thepower generation system's working fluids CO2 and H2O, and furtherwherein the power generation system operates as an essentially closedsystem with respect to the materials CO2, H2, O2, H2O, and hydrocarbons,such that essentially none of these materials pass through the boundaryof the power generation system into or out of its interior during normaloperation of the power generation system.
 27. The controllable powergeneration system of claim 26, wherein all of the at least onehydrocarbon fuel used is produced within the boundary enclosing theinterior of the power generation system, starting from an initialloading of CO2, H2, O2, and H2O.